Megacab + Lumber Rack = Howl HELP!

[AMink]

From another thread I posted:

Well, I got a Kargo Master rack. Sturdy and at what I think was a good price. I like that it has three cross members. I don't like that it howls like a big dog going down the highway. I had to get one that is made to go over a shell, so it sticks out on the sides. They said the regular one wouldn't clear the cab. Apparently, it is a little taller than a quadcab or other 4 door cabs. It doesn't quite get to the front of the roof, and I think that's why it howls. I'll probably be taking it back, as the guy at the shop said it shouldn't make any noise. Is this a common issue with lumber racks?

Didn't get any responses, so I ask for help again. Has anyone else had this issue? What is a good way to minimize this noise? The dealer spoke to Kargomaster and they said even if the rack was extended past the front of the roof, it will still howl. There are some deflectors that I can get, but would like other opinions. I am going to keep the rack, as I'm sure one or more of you smart-type folks have a solution. Thanks!

 

[JoshPeters]

In all the years I've built and used ladder racks, I've never had the rack itself howl. The Ladders on it... definatly. Are the ends of the cross supports open? Block them off with something. The venturi effect on both ends is like a coke bottle.

 

[AMink]

All the ends are closed. The explanation I got was that since the front of the rack is over the cab (6"-8" behind the top of the windshield), the air going over and under the pipe is hitting the roof, thus causing the noise. Most racks that I've seen extend past the roof, but they say that won't help on the Mega because the roof itself is so long . I don't get it. It is most noticeable at freeway speed (of course!) or when the wind is blowing against the direction of travel. I can see a little noise because of the lack of aerodynamics, but this gets loud and annoying.

 

[JoshPeters]

Just for an exparament... .

Take a piece of cardboard and some duct tape, make an airfoil from the tube to the cab.

See if the noise goes away.

It's worth a shot. If it works, I'm sure something better could be built.

 

[AMink]

That's a good idea. I was trying to think what I could use for testing. I hate to have anything touch the cab, but for short term it probably won't hurt. If nothing else, it will tell me if that's really where the noise is coming from. Could be one of the other pieces and the sound is transmitting through the frame of the rack. Maybe fill it with expansive foam to dampen the vibrations.